Research Institute of Highway

Vehicle loads constitute the dominant source of dynamic excitation for small- and medium-span bridges, exerting a critical influence on bridge safety and service performance. However, vehicle load characteristics exhibit pronounced temporal variability and strong regional heterogeneity, which poses challenges for accurately characterizing the in-service loading conditions of bridges in specific regions using conventional dynamic load models. Therefore, this study focuses on the actual operational characteristics of vehicles on the Lieshihe bridge and the effects of vehicle loads and proposes a stochastic vehicle load simulation method based on the Monte Carlo sampling technique and weigh-in-motion (WIM) measured data. Initially, the recorded vehicle data are classified into representative vehicle models, and statistical analyses are conducted to characterize lane-dependent traffic flow variations and the occurrence patterns of vehicle overloading. Subsequently, axle number and axle spacing are selected as the core indicators for vehicle classification, based on which vehicles are categorized into five representative vehicle types. The changing patterns of axle load, vehicle weight, vehicle speed, etc., for each vehicle type are studied, and corresponding probability density distribution models are established to describe the stochastic nature of vehicle characteristics. Finally, using the Monte Carlo method combined with important attributes of vehicle flows, a stochastic vehicle load model is established based on the spatial-temporal characteristics. The results demonstrate that the vehicle weight on the bridge exhibits a Gaussian mixture distribution with multi-peaks, characterized by similar peak magnitudes but markedly different occurrence frequencies; axle load shows a single-peak distribution of Gaussian distribution with small differences in peak values and frequencies.

Abstract To address the problem of significant performance variability in SBS-modified asphalt recovered by the conventional centrifugal extraction-Abuson distillation method, this study systematically analyzed the key influencing factors of the recovery process and proposed corresponding improvement measures. Through blank and comparative experiments, the effects of mineral powder, trichloroethylene residue, and the distillation process on the evaluation of SBS-modified asphalt properties were investigated. The results show that small amounts of mineral powder (≤1.5%) have a slight hardening effect on modified asphalt, but the impact on overall performance is limited. Trichloroethylene residue is the main factor causing performance deviation of recovered asphalt; even a 0.2% residue can increase the ductility by 36%. The conventional Abuson distillation method has incomplete trichloroethylene removal due to solvent reflux, leading to softening of recovered asphalt and a viscosity variation coefficient of up to 23.6%. An improved recovery method combining Abuson distillation with vacuum drying (vacuum degree 94.7 kPa, heating temperature 170℃, evaporation time 1.5h) was proposed. The performance variation coefficients of recovered asphalt are all less than 5%. This improved method can accurately recover SBS-modified asphalt and provide technical support for the performance evaluation of old modified asphalt.

To address the impact of environmental and equipment factors on signal identification in highway tunnel drainage pipeline blockage monitoring, this study aims to elucidate the influence patterns of pipeline flow rate, optical fiber deployment scheme, and fiber performance on blockage-induced acoustic signals. A full-scale concrete pipeline experimental platform was established. Data were acquired using a HIFI-DAS V2 sensing system. The time–frequency domain characteristics of acoustic signals under different flow rates (50 m3/h and 100 m3/h), fiber deployment schemes (inside the pipe, outside the pipe, and outside a soundproofing layer), and fiber materials (six typical types) were analyzed and compared. The degree of influence of each factor on signal amplitude and dominant frequency components was quantified. The experimental results indicate that: Compared to a flow rate of 50 m3/h, the amplitude characteristic value at the blockage channel exhibited a marked increase at 100 m3/h, accompanied by an increase in the number and amplitude of dominant frequency components. While the dominant frequency components of the acoustic signals were less stable across the three deployment schemes, the overall amplitude at the blockage channel was consistently higher than that at non-blockage channels. When the fiber was deployed farther from the fluid core (outside the soundproofing layer), the dominant frequencies essentially disappeared, with energy distributed in a broadband form. The peak amplitude and array energy of the sensitive vibration sensing fiber were 2 times and 3.6 times those of the worst-performing type, respectively. Furthermore, its physical properties are better suited to the tunnel environment, effectively enhancing signal acquisition stability and the signal-to-noise ratio. Comprehensive analysis demonstrates that deploying sensitive fibers inside the pipe is more conducive to the accurate identification of blockage events. Moreover, uniform dominant frequency components and threshold criteria are not recommended along the entire length of the drainage pipe. This research provides theoretical and experimental support for parameter optimization of DAS systems to achieve high-precision pipeline blockage monitoring in complex tunnel environments.

Flood factors are key parameters affecting the hydraulic characteristics at a bridge site. Clarifying the development patterns and impacts of flood factors at a bridge site is of great significance for the stability assessment and service safety of bridges. Therefore, the impact analysis of flood factors, i.e., the initial flow velocity, scour angle, scour depth, on the evolution pattern of hydraulic characteristics at a bridge site is numerically conducted in this research. The structural model and hydraulic model are first established for numerical analysis. The correctness of models is verified through the existing analytical formula and experimental result. The evolution patterns of hydraulic characteristics at a bridge site are systematically evaluated. The results show that the flow velocity at the upstream side of the bridge exhibits relatively uniform and continuous distribution in both transverse and vertical directions, primarily caused by the obstruction of bridge piers. At the downstream side of the bridge, the flow velocity presents non-uniform development, induced by the horseshoe vortex and flow disturbance near the upstream pier. The coupling effect of the lateral flow velocity component suppressing vertical vortices and complex flow separation induces the distinct flow velocity distributions. Scour depth alters the flow field patterns, thereby influencing the flow’s resistance and acceleration properties. The above development pattern of hydraulic characteristics at the bridge site holds practical significance for conducting detailed analyses of flood impacts on bridges.

This study investigated the noise reduction performance of porous asphalt concrete (PAC) pavement under tire–pavement coupling conditions, addressing the limitations of field measurements and laboratory testing. First, tire excitation amplitude parameters were determined based on vibrational contact operational scenarios. Then, finite element simulations were conducted to systematically analyzing the tire–pavement coupling noise characteristics of PAC pavement. The results indicate that PAC pavement effectively reduces the air pumping noise due to its highly porous internal structure, leading to significant noise attenuation. Furthermore, the study examined the key factors influencing the tire–pavement coupling noise in PAC pavement. When maintaining constant vehicle parameters (300 kg load, 60 km/h speed), pavement thickness became the critical noise-control variable, achieving minimum vibration at 6 cm surface layer thickness. Additionally, tire tread depth (5–17 mm) and mold release angle (0–30°) had a more pronounced impact on the air pumping noise compared to groove width (20–60 mm). Increasing the mold release angle and reducing tread depth effectively mitigated the air pumping noise. However, the tire–pavement coupling noise in PAC pavement increased considerably with increasing vehicle speed and load. Particularly, as the speed increased from 30 km/h to 60 km/h, the growth of the air pumping noise was most pronounced, revealing an acoustic transition of tire–pavement coupling noise from vibration-dominated to air-pumping-dominated mechanisms.

In desert edge areas, the degree of soil salinization is high, and aeolian sand contains a significant amount of fines. As fine‐grained aeolian sand is more susceptible to temperature, moisture, and salt influences compared to pure aeolian sand, its use in road construction may induce roadbed diseases at later stages. To investigate the mechanical properties of fine‐grained salinized aeolian sand in seasonally frozen desert edges, laboratory triaxial unconsolidated undrained shear tests were performed on specimens with varying freeze‐thaw (FT) cycles (0–9 times), confining pressures (50–150 kPa), and fine contents (0%–16%). The study examined stress–strain relationships and shear strength variations in FT cycles. Additionally, scanning electron microscopy was employed to analyze microstructural changes in particle contact states before and after FT cycles. The concept of shear strength deterioration was introduced to quantify strength decay rates, and a predictive model incorporating both FT cycles and fines content was developed. Results indicate that stress–strain behavior shifts from strain softening to weak softening with increasing FT cycles, particularly at higher fines content. Shear strength declined hyperbolically with FT cycles and linearly with fines content, with a 34.4% reduction observed for 16% fines after 9 cycles. Microstructural analysis showed fines and salt crystals fill pores initially but degrade under FT, weakening particle bonds. The findings provide valuable references for road engineering construction in desert‐edge salinized aeolian sand regions.